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DNS problem on Migration (Centos 7 to 8)

Good day everybody.
I am trying to migrate Zimbra 7.13 to Zimbra 8 on CentOS and I have the following problem, causing me absolute nightmares:

1. Creating a second server CentOS 6.3 (Final) and starting the Split DNS on it, causes my mailq on my main server to defer all my mail.
2. Stopping the NEW SERVER's network does not improve the scenario.
3. The MAIN SERVER keeps on reporting on my DIG COMMAND: "connection timed out; no servers could be reached".
4. The mail-logs reports: Host or domain name not found. Name service error for name=<MY HOST> type=A not found, try again and,
5. delivery temporarily suspended: Host or domain name not found. Name service error for name=<ISP HOST> type=MX: Host not found, try again

My question is this:
1. How do I duplicate my "SplitDNS" environment so that I can install ZIMBRA 7.13 on a new CentOS 6.3 Server?
2. AND HOW DO I FIX THE MAIL NOT FLOWING? It takes for ever to deliver mail once I get into this DNS Problem...

Kind regards
Aubrey Kloppers
ps - It does not help reading the WIKI, there is nothing that I have not tried...

You can't have two mail servers running with the same domain names and expect mail to flow into both of them, think about it. It would also depend on which instructions your following to move from one server to another. As a general comment with the limited information you've given you would want to use a Split Domain to have both servers running at the same time.

Hi Bill
(Long time no write!)
Yes, the SLIT DNS is running on both the servers. Both servers have been configured EXACTLY the same.

Comparing the two servers:
1. /etc/hosts the same (but for the local mail server ip numbers)
2. /etc/resolv.conf the same
3. /etc/named.conf the same (except for the "listen on" internal IP numbers)
4. /etc/named/* files the same (except for the ip numbers in the various config files)

Notes:
Both the servers can reach the Internet
Both Server's MX DIG shows the correct info for the servers.

What I attempt doing:
1. Get both the server on 7.1.3 (ORIGINAL on CentOS5.n, NEW on CentOS 6.4).
2. rsync the /opt/zimbra from ORIGINAL to NEW.
3. Once everything is sync'ed, take down the ORIGINAL and bring up the NEW. (after copying the /etc/hosts and /etc/named/ and /etc/named.conf files)
4. Upgrade the NEW to Zimbra 8.

I hope you understand
Kind regards
Aubrey Kloppers
Bible Society of SA
Cape Town
South Africa